add slots

Author: donbarbos

stubs/psutil/psutil/_pswindows.pyi

@@ -193,6 +193,7 @@ if sys.platform == "win32":
     def retry_error_partial_copy(fun): ...
 
     class Process:
+        __slots__ = ["_cache", "_name", "_ppid", "pid"]
         pid: int
         def __init__(self, pid: int) -> None: ...
         def oneshot_enter(self) -> None: ...